Endoscope structures and techniques for navigating to a target in a branched structure

ABSTRACT

Systems and methods employing a small gauge steerable catheter including a locatable guide with a sheath, particularly as an enhancement to a bronchoscope. A typical procedure is as follows. The location of a target in a reference coordinate system is detected or imported. The catheter is navigated to the target which tracking the distal tip of the guide in the reference coordinate system. Insertion of the catheter is typically via a working channel of a convention bronchoscope. Once the tip of the catheter is positioned at the target, the guide is withdrawn, leaving the sheath secured in place. The sheath is then used as a guide channel to direct a medical tool to target.

RELATED APPLICATIONS

The present application is a divisional application of U.S. patentapplication Ser. No. 14/250,738 filed Apr. 11, 2014 entitled EndoscopeStructures and Techniques for Navigating to a Target in BranchedStructure, which is a continuation of U.S. patent application Ser. No.12/723,577 filed Mar. 12, 2010 entitled Endoscope Structures andTechniques for Navigating to a Target in Branched Structure, which is acontinuation of U.S. patent application Ser. No. 11/765,330 filed Jun.19, 2007 entitled Endoscope Structures and Techniques for Navigating toa Target in Branched Structure (now U.S. Pat. No. 7,998,062 issued Aug.16, 2011), which is a continuation of U.S. patent application Ser. No.10/491,099 filed Mar. 29, 2004 entitled Endoscope Structures AndTechniques For Navigating To A Target In Branched Structure (now U.S.Pat. No. 7,233,820 issued Jun. 19, 2007); which claims benefit ofInternational Patent Application No. PCT/IL03/00323, InternationalFiling Date 16 Apr. 2003, entitled Endoscope Structures And TechniquesFor Navigating To A Target In Branched Structure, which claims benefitof U.S. Provisional Application Ser. No. 60/372,804 filed Apr. 17, 2002entitled Navigate A Catheter In The Bronchial Tree; U.S. ProvisionalApplication Ser. No. 60/388,758 filed Jun. 17, 2002 entitled IndependentWorking Channel For Bronchoscope And Method Of Use; and U.S. ProvisionalApplication Ser. No. 60/407,951 filed Sep. 5, 2002 entitled DesignatingA Target And Navigating A Tool Using A Fluoroscope And An Endoscope; allof which are incorporated in their entirety herein by reference.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates to endoscopes and, in particular, itconcerns endoscope structures and techniques for navigating to a targetin branched structure, such as the human lungs, and for bringing amedical tool to the target.

Biopsy taken from suspected malignant tissue inside the bronchial treeis conventionally performed using a bronchoscope. The bronchoscope,which is a type of endoscope, is a flexible tube having a miniaturecamera at its tip. Actuated from a handle at its proximal end, its tiphas the ability to deflect in two opposite directions, allowing it to besteered inside the bronchial tree. The bronchoscope also has a workingchannel, typically of internal diameter about 2.8 mm, allowing a toolsuch as a biopsy forceps to be inserted and driven ahead of its distaltip.

Once unidentified lung mass is discovered in a CT scan, a biopsy of thismass should be taken. The patient is positioned on an operating table, abronchoscope is inserted into the bronchial tree and directed towardsthe mass. Once the tip of the bronchoscope is placed in contact with themass, as validated by direct viewing of the mass in the bronchoscopeimage, a forceps is pushed via the working channel into the mass andbiopsy is taken.

While this technique is straightforward in principle, the practicalapplication is often highly problematic. The air paths of the bronchialtree get progressively narrower as they branch with increasing depthinto the bronchial tree. A typical bronchoscope is a two- or three-lumenstructure (including fiber bundles for imaging and illumination andworking channel for suction and/or tools) and is typically around 5 or 6millimeters in diameter. In consequence, a bronchoscope can reach onlythe third, or at most the fourth, bifurcation level of the tree(indicated by a dashed circle in FIG. 24). If the mass is at theperiphery of the tree, the biopsy forceps must be pushed further aheadof the tip of the bronchoscope in the estimated direction of the mass.The biopsy itself is then taken blindly. X-ray fluoroscopic imaging isoften used as a visual aid, but this is only of any value for relativelylarge masses visible under a fluoroscope, and the two-dimensional imagesproduced are a poor navigation aid, lacking depth perception. For theseand other reasons, it is estimated that more than 60% of the totalnumber of bronchial biopsies are taken mistakenly in a wrong location.

Various devices have been proposed in order to try to ameliorate thelimitations of bronchoscopes. Of particular interest is U.S. Pat. No.4,586,491 to Carpenter which discloses a bronchoscope with a small gaugeviewing attachment. The viewing attachment is selectively advanced pastthe end of the bronchoscope to view tissue beyond the reach of the mainbronchoscope shaft.

Although the device of Carpenter allows viewing of tissue withinpassageways too narrow for the bronchoscope to enter, it is very limitedin its usefulness. Firstly, the viewing attachment is not steerable,relying instead on the pointing direction of the end of thebronchoscope. As a result, the viewing attachment is limited in itscapabilities to reach target tissue. Secondly, the system provides nolocation information to facilitate navigation to the target tissue.Finally, the device is of little or no use for navigating a medical toolto the target location. If the viewing attachment is removed to allowintroduction of a tool to the working channel, manipulation of the toolmust again be performed “blindly” without any guarantee that the correcttarget tissue has been reached.

There is therefore a need for endoscopes and corresponding methods whichfacilitate navigation to a target within a branched structure such asthe bronchial tree, and which allows a medical tool to be broughtaccurately to the target.

SUMMARY OF THE INVENTION

The present invention provides endoscope structures and correspondingtechniques for navigating to a target in branched structure, such as thehuman lungs, and for bringing a medical tool to the target.

According to the teachings of the present invention there is provided, amethod for steering a catheter through a branched structure to a targetlocation, the method comprising: (a) providing a flexible, steerablecatheter with a position sensor element located near a distal tip of thecatheter, the position sensor element being part of a position measuringsystem measuring a position and a pointing direction of the tip of thecatheter relative to a three-dimensional frame of reference; (b)designating the target location relative to the three-dimensional frameof reference; (c) advancing the catheter into the branched structure;and (d) displaying a representation of at least one parameter defined bya geometrical relation between the pointing direction of the tip of thecatheter and a direction from the tip of the catheter towards the targetlocation.

According to a further feature of the present invention, the at leastone parameter includes an angular deviation between the pointingdirection of the tip of the catheter and a direction from the tip of thecatheter towards the target location.

According to a further feature of the present invention, the at leastone parameter includes a direction of deflection required to bring thepointing direction of the catheter into alignment with the targetlocation.

According to a further feature of the present invention, therepresentation of at least one parameter is displayed in the context ofa representation of a view taken along the pointing direction of the tipof the catheter.

According to a further feature of the present invention, the positionsensor element is part of a six-degrees-of-freedom position measuringsystem measuring the position and attitude of the tip of the catheter inthree translational and three rotational degrees of freedom.

According to a further feature of the present invention, the catheter isfurther provided with a multi-directional steering mechanism configuredfor selectively deflecting a distal portion of the catheter in any oneof at least three different directions.

According to a further feature of the present invention, a path traveledby the tip of the catheter is monitored by use of the position sensorelement and a representation of the path traveled is displayed togetherwith a current position of the tip, the representation being projectedas viewed from at least one direction non-parallel to the pointingdirection of the tip.

According to a further feature of the present invention, the designatingthe target location is performed by: (a) designating a target locationby use of computerized tomography data generated from the branchedstructure; and (b) registering the computerized tomography data with thethree-dimensional frame of reference.

According to a further feature of the present invention, the registeringis performed by: (a) providing the steerable catheter with a camera; (b)generating a camera view of each of at least three distinctive featureswithin the branched structure; (c) generating from the computerizedtomography data a simulated view of each of the at least threedistinctive features, each camera view and a corresponding one of thesimulated views constituting a pair of similar views; (d) allowing anoperator to designate a reference point viewed within each of the cameraviews and a corresponding reference point viewed within eachcorresponding simulated view; and (e) deriving from the designatedreference points a best fit registration between the computerizedtomography data and the three-dimensional frame of reference.

According to a further feature of the present invention, an intendedroute through the branched structure is designated by use of thecomputerized tomography data and a representation of the intended routeis displayed together with a current position of the tip, therepresentation being projected as viewed from at least one directionnon-parallel to the pointing direction of the tip.

According to a further feature of the present invention: (a) a currentposition of the position sensor element is detected; (b) a virtualendoscopy image is generated from the computerized tomography datacorresponding to an image that would be viewed by a camera located inpredefined spatial relationship and alignment relative to the positionsensor element; and (c) displaying the virtual endoscopy image.

According to a further feature of the present invention, the branchedstructure is a lung structure.

According to a further feature of the present invention, measurements ofthe position and pointing direction of the tip of the catheter areprocessed so as to reduce variations resulting from cyclic motion.

According to a further feature of the present invention, the processingincludes selectively taking measurements at an extreme of a cyclicmotion.

According to a further feature of the present invention, the processingincludes applying a low-frequency filter to the measurements.

According to a further feature of the present invention, the processingincludes calculating an average of the measurements over a time periodof the cyclic motion.

According to a further feature of the present invention, the steerablecatheter further includes: a sheath having a lumen extending from aproximal insertion opening to a distal opening; and a guide elementconfigured for insertion through the proximal opening of the sheath toan inserted position extending along the lumen to the distal opening,the guide element including at least part of an imaging system deployedfor taking optical images of a region beyond the distal opening, themethod further comprising: (a) guiding the steerable catheter to aposition with the tip adjacent to the target location; and (b)withdrawing the guide element from the lumen to leave the lumenavailable for insertion of a medical tool.

According to a further feature of the present invention, a medical toolis prepared for insertion into the lumen by: (a) inserting the medicaltool into a calibration tube, the calibration tube having a lengthcorresponding to a length of the lumen; and (b) marking an extent ofinsertion on the tool.

According to a further feature of the present invention, the calibrationtube is a coiled storage tube employed to store the guide element priorto use, the guide element being removed from the storage tube prior toinserting the tool.

According to a further feature of the present invention, the steerablecatheter further includes a handle having a working channel, a sheathdeployed within the working channel and having an internal lumen, and aguide element including the position sensor element deployed within thelumen, the method further comprising: (a) locking the guide elementwithin the sheath so as to prevent movement of the guide elementrelative to the sheath; (b) guiding the sheath and the guide element tothe target location; (c) locking the sheath within the working channelto prevent relative movement of the sheath relative to the handle; and(d) unlocking and withdrawing the guide element from the sheath so as toleave the lumen of the sheath in place as a guide for inserting a toolto the target location.

According to a further feature of the present invention, a selectivelyactuatable anchoring mechanism is associated with a portion of thesheath.

According to a further feature of the present invention, the selectivelyactuatable anchoring mechanism includes an inflatable element.

According to a further feature of the present invention, the selectivelyactuatable anchoring mechanism includes a mechanically deployed element.

According to a further feature of the present invention, the guideelement further includes an image sensor deployed for generating animage in the pointing direction of the catheter, the image sensor beingwithdrawn from the sheath as part of the guide element.

According to a further feature of the present invention, at least partof the location sensor is formed from translucent material, the methodfurther comprising illuminating at least part of a field of view of theimage sensor by directing illumination through at least one region ofthe translucent material.

According to a further feature of the present invention, at least partof a field of view of the image sensor is illuminated by using at leasta distal portion of the sheath as an optical waveguide.

According to a further feature of the present invention, illumination issupplied to the optical waveguide from at least one light source mountedwithin the guide element.

According to a further feature of the present invention, illumination issupplied to the optical waveguide from at least one light sourceassociated with the handle.

According to a further feature of the present invention, the guideelement further includes a radioactivity sensor, the sensor beingwithdrawn from the sheath as part of the guide element.

According to a further feature of the present invention, the steerablecatheter is a flexible endoscope.

According to a further feature of the present invention, the steerablecatheter is a flexible bronchoscope.

There is also provided according to the teachings of the presentinvention, a method for achieving registration between computerizedtomography data and a three dimensional frame of reference of a positionmeasuring system, the method comprising: (a) providing a catheter with:(i) a position sensor element which operates as part of the positionmeasuring system to allow measurement of a position and a pointingdirection of the tip of the catheter relative to the three-dimensionalframe of reference, and (ii) an image sensor; (b) generating from thecomputerized tomography data at least three simulated views ofdistinctive features within the branched structure; (c) generating atleast three camera views of the distinctive features, each camera viewand a corresponding one of the simulated views constituting a pair ofsimilar views; (d) allowing an operator to designate a reference pointviewed within each of the camera views and a corresponding referencepoint viewed within each corresponding simulated view; and (e) derivingfrom the designated reference points a best fit registration between thecomputerized tomography image and the three-dimensional frame ofreference.

According to a further feature of the present invention, designation ofa reference point within each of the camera views by the operator isperformed by the operator bringing the position sensor element intoproximity with the reference point.

According to a further feature of the present invention, designation ofa reference point within each simulated view by the operator isperformed by: (a) the operator selecting a simulated image referencepoint within each simulated view; (b) calculating from the simulatedimage reference point a simulated-viewing-point-to-reference-pointvector; and (c) calculating a point of intersection between thesimulated-viewing-point-to-reference-point vector and a tissue surfacein a numerical model of a portion of the body derived from thecomputerized tomography data.

According to a further feature of the present invention: (a) at leastone location within the computerized tomography data is identified; (b)a position of the at least one location is calculated within thethree-dimensional frame of reference; and (c) a representation of the atleast one location is displayed together with a representation of aposition of the position sensor element.

According to a further feature of the present invention, the at leastone location includes a target location to which a medical tool is to bedirected.

According to a further feature of the present invention, the at leastone location is a series of locations defining a planned path alongwhich a medical tool is to be directed.

There is also provided according to the teachings of the presentinvention, a method for achieving registration between computerizedtomography data and a three dimensional frame of reference of a positionmeasuring system, the method comprising: (a) providing a catheter with:(i) a position sensor element which operates as part of the positionmeasuring system to allow measurement of a position and a pointingdirection of the tip of the catheter relative to the three-dimensionalframe of reference, and (ii) an image sensor; (b) moving the tip of thecatheter along a first branch portion of a branched structure andderiving a plurality of images from the camera, each image beingassociated with corresponding position data of the position sensor inthe three dimensional frame of reference; (c) processing the images andcorresponding position data to derive a best-fit of a predefinedgeometrical model to the first branch portion in the three dimensionalframe of reference; (d) repeating steps (b) and (c) for a second branchportion of the branched structure; and (e) correlating the geometricalmodels of the first and second branch portions with the computerizedtomography data to derive a best fit registration between thecomputerized tomography data and the three dimensional frame ofreference.

According to a further feature of the present invention, the processingthe images and corresponding position data includes: (a) identifyingvisible features each of which is present in plural images taken atdifferent positions; (b) for each of the visible features, deriving acamera-to-feature direction in each of a plurality of the images; (c)employing the camera-to-feature directions and corresponding positiondata to determine a feature position for each visible feature; and (d)deriving a best-fit of the predefined geometrical model to the featurepositions.

According to a further feature of the present invention, the predefinedgeometrical model is a cylinder.

According to a further feature of the present invention: (a) at leastone location within the computerized tomography data is identified; (b)a position of the at least one location within the three-dimensionalframe of reference is calculated; and (c) a representation of the atleast one location is displayed together with a representation of aposition of the position sensor element.

According to a further feature of the present invention, the at leastone location includes a target location to which a medical tool is to bedirected.

According to a further feature of the present invention, the at leastone location is a series of locations defining a planned path alongwhich a medical tool is to be directed.

There is also provided according to the teachings of the presentinvention, an endoscope for guiding a medical tool to a target location,the endoscope comprising: (a) a sheath having a lumen extending from aproximal insertion opening to a distal opening; (b) a guide elementconfigured for insertion through the proximal opening of the sheath toan inserted position extending along the lumen to the distal opening,the guide element including at least part of an imaging system deployedfor taking optical images of a region beyond the distal opening; and (c)at least one steering mechanism for co-deflecting the sheath and theguide element, wherein the guide element is retractable from the lumento leave the lumen available for insertion of a medical tool.

According to a further feature of the present invention, the at leastpart of an imaging system includes an optical sensor chip deployed at adistal end of the guide element.

According to a further feature of the present invention, the guideelement includes a position sensor element, the position sensor elementbeing part of a position measuring system measuring a position and apointing direction of a tip of the guide element relative to athree-dimensional frame of reference.

According to a further feature of the present invention, at least partof the position sensor element is formed from translucent material, theendoscope further comprising an illumination arrangement deployed todirect illumination through at least one region of the translucentmaterial so as to illuminate at least part of the region beyond thedistal opening.

According to a further feature of the present invention, there is alsoprovided a selectively actuatable anchoring mechanism associated with aportion of the sheath.

According to a further feature of the present invention, the selectivelyactuatable anchoring mechanism includes an inflatable element.

According to a further feature of the present invention, the selectivelyactuatable anchoring mechanism includes a mechanically deployed element.

According to a further feature of the present invention, at least adistal part of the sheath is substantially radio-opaque.

According to a further feature of the present invention, there is alsoprovided at least one radio-opaque marked associated with a distal endof the sheath.

According to a further feature of the present invention, at least adistal portion of the sheath is implemented as an optical waveguide.

According to a further feature of the present invention, there is alsoprovided at least one light source mounted within the guide element forilluminating at least part of the region beyond the distal opening.

According to a further feature of the present invention, there is alsoprovided at least one optical fiber deployed along the length of theguide element for delivering illumination to at least part of the regionbeyond the distal opening.

According to a further feature of the present invention, the guideelement further includes a radioactivity sensor, the sensor beingwithdrawn from the sheath as part of the guide element.

There is also provided according to the teachings of the presentinvention, a method of guiding a medical tool through a branchedstructure to a target location, the method comprising: (a) providing acatheter assembly including a handle having a working channel, a sheathdeployed within the working channel and having an internal lumen, and aguide element deployed within the lumen; (b) locking the guide elementwithin the sheath so as to prevent movement of the guide elementrelative to the sheath; (c) guiding the sheath and the guide element tothe target location; (d) locking the sheath within the working channelto prevent relative movement of the sheath relative to the handle; and(e) unlocking and withdrawing the guide element from the sheath so as toleave the lumen of the sheath in place as a guide for inserting a toolto the target location.

There is also provided according to the teachings of the presentinvention, the guide element includes a position sensor element, theposition sensor element being part of a position measuring systemmeasuring a position and a pointing direction of a tip of the guideelement relative to a three-dimensional frame of reference.

There is also provided according to the teachings of the presentinvention, a selectively actuatable anchoring mechanism is associatedwith a portion of the sheath.

There is also provided according to the teachings of the presentinvention, the selectively actuatable anchoring mechanism includes aninflatable element.

There is also provided according to the teachings of the presentinvention, the selectively actuatable anchoring mechanism includes amechanically deployed element.

There is also provided according to the teachings of the presentinvention, at least a distal part of the sheath is treated so as to besubstantially radio-opaque.

There is also provided according to the teachings of the presentinvention, at least one radio-opaque marked is associated with a distalend of the sheath.

There is also provided according to the teachings of the presentinvention, the guide element further includes an image sensor deployedfor generating an image in the pointing direction of the catheter, theimage sensor being withdrawn from the sheath as part of the guideelement.

There is also provided according to the teachings of the presentinvention, a field of view of the image sensor is illuminated by usingat least a distal portion of the sheath as an optical waveguide.

There is also provided according to the teachings of the presentinvention, illumination is supplied to the optical waveguide from atleast one light source mounted within the guide element.

There is also provided according to the teachings of the presentinvention, illumination is supplied to the optical waveguide from atleast one light source associated with the handle.

There is also provided according to the teachings of the presentinvention, the guide element further includes a radioactivity sensor,the sensor being withdrawn from the sheath as part of the guide element.

There is also provided according to the teachings of the presentinvention, a steering mechanism for selectively deflecting a distalportion of a steerable catheter in any one of at least two independentdirections, the mechanism comprising: (a) at least three elongatedtensioning elements extending along the catheter and configured suchthat tension applied to any one of the tensioning elements causesdeflection of a tip of the catheter in a corresponding predefineddirection; (b) an actuator displaceable from a first position to asecond position; and (c) a selector mechanism configured for selectivelymechanically interconnecting a selected at least one of the elongatedtensioning elements and the actuator such that displacement of theactuator from the first position to the second position applies tensionto the selected at least one of the elongated tensioning elements.

According to a further feature of the present invention, a first stateof the selector mechanism mechanically interconnects a single one of theelongated tensioning elements with the actuator such that displacementof the actuator generates deflection of the tip in one of the predefineddirections, and a second state of the selector mechanism mechanicallyinterconnects two of the elongated tensioning elements with the actuatorsuch that displacement of the actuator generates deflection of the tipin an intermediate direction between two of the predefined directions.

According to a further feature of the present invention, the at leastthree tensioning elements includes an even number of the tensioningelements, pairs of the tensioning elements being implemented as a singleelongated element extending from the selector mechanism along thecatheter to the tip and back along the catheter to the selectormechanism.

According to a further feature of the present invention, the at leastthree tensioning elements is implemented as four tensioning elementsdeployed such that each tensioning element, when actuated alone, causesdeflection of the tip in a different one of four predefined directionsseparated substantially by multiples of 90.degree.

According to a further feature of the present invention, a first stateof the selector mechanism mechanically interconnects a single one of theelongated tensioning elements with the actuator such that displacementof the actuator generates deflection of the tip in one of the fourpredefined directions, and a second state of the selector mechanismmechanically interconnects two of the elongated tensioning elements withthe actuator such that displacement of the actuator generates deflectionof the tip in one of four intermediate directions each lying between twoof the four predefined directions.

According to a further feature of the present invention, the actuatorincludes a ring which is slidable relative to a handle associated withthe catheter, and wherein the selector mechanism includes a slideattached to each of the tensioning elements and slidably deployed withinthe handle and at least one projection projecting from the ring suchthat, when the ring is rotated, the at least one projection selectivelyengages at least one of the slides such that displacement of the ringcauses movement of the at least one slide.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention is herein described, by way of example only, withreference to the accompanying drawings, wherein:

FIG. 1 is a schematic overall representation of a system, constructedand operative according to the teachings of the present invention, fornavigating to a target within a branched structure;

FIG. 2 is a schematic side view of a steerable catheter, constructed andoperative according to the teachings of the present invention, for usein the system of FIG. 1;

FIG. 3 is a schematic isometric view of a tip portion of the catheter ofFIG. 2;

FIGS. 4A and 4B are schematic cross-sectional views through a steeringmechanism controller from the catheter of FIG. 2 in a non-actuatedstate, and an actuated state, respectively;

FIGS. 5A-5C are cross-sectional views taken along the line V-V in FIG.4A showing a steering direction selector in first, second and thirdpositions, respectively;

FIG. 6A is a schematic isometric view showing the hand position of apractitioner during selection of a steering direction of the catheter ofFIG. 2;

FIG. 6B is a schematic isometric view showing the hand position of apractitioner during navigation of the catheter of FIG. 2;

FIG. 7 is a schematic cross-sectional view of an alternativeimplementation of the tip portion of the catheter of FIG. 2 including animage sensor;

FIG. 8 is a schematic isometric view illustrating an arrangement foracquiring a target location in a position sensor frame of referenceusing isotopic labeling and an external detector;

FIG. 9 is a block diagram illustrating a procedure for acquiring atarget location using an external detector such as in the arrangement ofFIG. 8;

FIG. 10 is a block diagram illustrating a first procedure according tothe present invention for correlating CT data with a locationmeasurement system;

FIG. 11 is a display screen from a CT-based virtual bronchoscopy systemincluding a simulated view of the carina between the main left and rightbronchi for designation of a fiducial point for the procedure of FIG.10;

FIG. 12A is a bronchoscope view of the carina similar to the simulatedview of FIG. 11;

FIG. 12B is a view similar to FIG. 12A after the bronchoscope has beenadvanced to bring a location sensor into proximity with a point on thecarina for use as a fiducial point in the procedure of FIG. 10;

FIG. 13 is a block diagram illustrating a second procedure according tothe present invention for correlating CT data with a locationmeasurement system;

FIGS. 14A and 14B are schematic representations of views from an imagesensor, such as that of the catheter of FIG. 7, showing an identifiablefeature on the wall of a vessel as viewed from two viewing positions;

FIGS. 15A and 15B are schematic side views of the viewing positions ofthe tip of the catheter within part of a branched structure from whichthe views of FIGS. 14A and 14B, respectively, are obtained;

FIG. 16 is a schematic side view of the part of the branched structureindicating the determination of a location of the identifiable featureby triangulation;

FIGS. 17A and 17B are schematic illustrations of a tip-to-target displayat two stages during navigation of the catheter of FIG. 2 or FIG. 7towards a target;

FIGS. 18A, 18B and 18C are additional tip-to-target displays insagittal, AP and axial representations, respectively;

FIG. 19 is a display screen which combines the tip-to-target display ofFIG. 17A with dynamic CT-based displays corresponding to axial, sagittaland AP planes passing through the current catheter tip position;

FIGS. 20A-20D are schematic representations explaining a localdistortion correction technique for correcting for body posture induceddistortion between the CT data and measured positions;

FIG. 21 is a schematic illustration of an alternative implementation ofthe distortion correction technique by use of a transformation operator;

FIG. 22 is a block diagram illustrating a preferred sequence of use ofthe endoscope according to the teachings of the present invention;

FIG. 23 is a schematic isometric view illustrating the use of a coiledstorage tube as a calibration tube for calibrating the length of a toolfor use in the endoscope of the present invention; and

FIG. 24 is a schematic AP representation of the human lungs indicatingby a dashed circle the region accessible to a conventional bronchoscope.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides endoscope structures and correspondingtechniques for navigating to a target in branched structure, such as thehuman lungs, and for bringing a medical tool to the target.

The principles and operation of endoscopes and navigation techniquesaccording to the present invention may be better understood withreference to the drawings and the accompanying description.

Before addressing the drawings directly, it will be helpful tounderstand that the present invention provides a system andcorresponding methods including multiple features each of which isbelieved to be patentable in its own right, and many of which may haveutility independent of the other features of the invention in contextsother than the context described herein. For clarity of presentation, aswell as to illustrate the synergy between the different aspects of theinvention when combined, the various features will be described hereinin the context of a combined system and accompanying proceduraltechniques with only a small number of variants described explicitly.The applicability of the various features of apparatus and methodsaccording to the present invention, and as defined by the appendedclaims, in other contexts will be self explanatory to one ordinarilyskilled in the art.

By way of general introduction, one primary aspect of the presentinvention, common to many of the aforementioned patentable features, isa structure and method which addresses the limitations of theconventional bronchoscope as discussed above by providing a small gaugesteerable catheter including a locatable guide within a sheath. Theoutline of a typical procedure using this catheter is as follows:

a. The location of a target in a reference coordinate system is detectedor imported.

b. The catheter is navigated to the target while tracking the distal tipof the guide in the reference coordinate system. Insertion of thecatheter is typically via a working channel of a conventionalbronchoscope.

c. Once the tip of the catheter is positioned at the target, the guideis withdrawn, leaving the sheath secured in place.

d. The sheath is then used as a guide channel to direct a medical toolto the target.

For clarity of presentation, the following description will besubdivided as follows. First, with reference to FIGS. 1-7, the preferredstructure of a catheter and the accompanying system constructed andoperative according to the teachings of the present invention will bedescribed. Then, with reference to FIGS. 8-16, various techniques foracquiring target locations within the reference coordinate system willbe discussed. With reference to FIGS. 17A-21, various navigation aids,navigation techniques and associated corrections will be described.Finally, with reference to FIGS. 22 and 23, various aspects of thepresent invention relating to the use of medical tools inserted via asheath will be discussed.

General Structure

Referring now to the drawings, FIG. 1 is a schematic overallrepresentation of a system, constructed and operative according to theteachings of the present invention, for navigating to a target within abranched structure;

Specifically, FIG. 1 shows a patient 10 lying on an operating table 12.A bronchoscope 14 is inserted into his lungs. Bronchoscope 14 isconnected to the monitoring equipment 16, and typically includes asource of illumination and an video imaging system. In certain cases,the device of the present invention may be used without a bronchoscope,as will be described below. A position measuring system monitors theposition of the patient 10, thereby defining a set of referencecoordinates. A particularly preferred position measuring system is a sixdegrees-of-freedom electromagnetic position measuring system accordingto the teachings of U.S. Pat. No. 6,188,355 and published PCTApplication Nos. WO 00/10456 and WO 01/67035. In this case, atransmitter arrangement 18 is implemented as a matt positioned beneathpatient 10. A number of miniature sensors 20 are interconnected with atracking module 22 which derives the location of each sensor 20 in 6 DOF(degrees of freedom). At least one, and preferably three, referencesensors 20 are attached to the chest of patient 10 and their 6 DOFcoordinates sent to a computer 24 where they are used to calculate thepatient coordinate frame of reference.

Also visible in FIG. 1 is a catheter assembly 30, constructed andoperative according to the teachings of the present invention, which isshown inserted via a working channel of bronchoscope 14. Catheterassembly 30 is shown more clearly in FIG. 2. Catheter assembly 30includes a locatable guide 32 which has a steerable distal tip 34, aflexible body 36 and, at its proximal end, a control handle 38. Guide 32is inserted into a sheath 40 within which it is locked in position by alocking mechanism 42. A position sensor element 44, operating as part ofthe position measuring system of FIG. 1, is integrated with distal tip34 and allows monitoring of the tip position and orientation (6 DOF)relative to the reference coordinate system.

Turning now to the steering mechanism of catheter 30, it should be notedthat the present invention may optionally be implemented with aconventional steering mechanism which provides a single direction ofdeflection. It has been found however that, due to the fine gauge of thecatheter and extensive area in contact with surfaces of the surroundinglumen, it becomes difficult to reliably turn the catheter about itslongitudinal axis to align the flexing direction with a desired steeringdeflection direction. To address this issue, the present inventionpreferably provides a multi-directional steering mechanism with a manualdirection selector which allows selection of a steering direction by thepractitioner without rotation of the catheter body. It should be notedthat the steering mechanism described herein is useful in a wide rangeof applications independent of the other features of the presentinvention, and is believed to be patentable in its own right.

Turning now to FIG. 3, this shows an enlarged view of distal tip 34 withposition sensor element 44 mounted on a base 46 to which at least three,and preferably four, elongated tensioning elements (“steering wires”) 48are attached. Steering wires 48 are deployed such that tension on eachwire individually will steer the tip towards a predefined lateraldirection. In the preferred case of four wires, the directions arechosen to be opposite directions along two perpendicular axes. In otherwords, the four wires are deployed such that each wire, when actuatedalone, causes deflection of said tip in a different one of fourpredefined directions separated substantially by multiples of 90.degree.For practical reasons of ease of manufacture and reliability, wires 48are preferably implemented as pairs of wires formed from a single longwire extending from handle 38 to tip 34, bent over part of base 46, andreturning to handle 38, as shown.

Referring now back to FIG. 2, and to the cross-sectional views of FIGS.4A-5C, handle 38 has an actuator, displaceable from a first position toa second position, and a selector mechanism for selectively mechanicallyinterconnecting at least one of the steering wires and the actuator suchthat displacement of said actuator from its first position to its secondposition applies tension to a selected one or more of steering wires 48.In the implementation shown here, the actuator is implemented as aslidable collar 50 which can be drawn rearwards relative to a fixedportion of handle 38. The selector mechanism is here implemented as bestseen in FIGS. 4A-5C as a rotational dial mechanism where a ridge,projection or step 52 on an internal surface of collar 50 selectivelyengages one or more slides, implemented here as actuator blocks 54 a,546, 54 c, 54 d, each of which is connected to a steering wire 48. Whencollar 50 is slid from its initial position (FIG. 4A) to its retractedposition (FIG. 4B), step 52 engages one or more actuator block (hereblock 54 a) so as to apply tension to the corresponding wire 48. Theremaining actuator blocks (only 54 c is visible in FIG. 4B) remain inplace.

FIGS. 5A-5C show an axial view of the selector mechanism in threedifferent states. In FIG. 5A, step 52 overlaps the actuator block 54 acorresponding to the steering wire for upward deflection of the guideelement. Clearance slots 56 ensure that the remaining actuator blocks 54b, 54 c, 54 d are not affected by sliding of collar 50. In FIG. 5B,collar 50 has been turned 45.degree. such that step 52 overlaps twoadjacent actuator blocks 54 a and 54 b. In this position, sliding ofcollar 50 applies tension to the corresponding two steering wires at thesame time, thereby causing deflection of distal tip 34 in anintermediate direction between the predefined primary directions. FIG.5C shows the selector mechanism after collar 50 has been turned througha further 45.degree. such that it now engages exclusively the actuatorblock 54 d on the left side of the figure as viewed.

It will be apparent that the structure described offers a highlycontrollable and easily operated steering mechanism in which a pluralityof steering wires provides selective deflection of the catheter tip inany of at least two independent directions. “Independent directions” arehereby defined in this context as flexing directions which arenon-coplanar. In the preferred example illustrated here, four steeringwires provide eight different steering directions, selectable by theturn of a dial, spaced at roughly 45.degree. increments. In a furthervariant implementation (not shown), the actuator and/or selectormechanism are configured to apply uneven tension on two wires so as toachieve additional intermediate steering directions or a substantiallycontinuously adjustable steering direction. A simple implementation ofsuch a mechanism employs a V-shaped actuator step such that mechanicalengagement with the actuator blocks occurs an adjustable axial distancefrom the rest position of the actuator.

Clearly, the mechanical implementation of the actuator and selectormechanism may vary considerably. Minor variations include implementationof the selector mechanism as a separate ring mounted in collar 50, andimplementation of step 52 as isolated inwardly-projecting engagementteeth rather than a near-continuous internal ridge. Other non-limitingexamples of possible variants include different implementations of theactuator such as by a trigger-type mechanism.

FIGS. 6A and 6B illustrate the ergonomic advantages of the preferredimplementation of the steering mechanism control as described. Afterinsertion of the distal tip (not shown) of the bronchoscope 14 as far asit can reach in the bronchial tree, catheter 30 is inserted into thebronchoscope's working channel via the working channel entrance 58. Theexternal diameter of sheath 40 is preferably slightly less than the 2.8mm diameter common in many bronchoscope working channels to facilitateinsertion via a standard bronchoscope. The catheter is then advancedbeyond the end of the bronchoscope towards the target. The handle 38 oflocatable guide 32 is configured to allow the practitioner to hold it,and operate the steering mechanism actuator, with the same hand(typically the left hand) with which he is holding the bronchoscope.This leaves his or her right hand free. To steer the guide in a desireddirection, collar 50 is rotated to select the direction in which theguide will be deflected (FIG. 6A). Then, while advancing the locatableguide into the working channel with the right hand, steering collar 50is retracted by squeezing together the fingers on collar 50 towards thethumb located at the rear of handle 38, as shown in FIG. 6B. Once thetip of the guide reaches the target, a locking arrangement 60 is lockedto stabilize sheath 40 relative to bronchoscope 14. Locking mechanism 42is then unlocked to release guide 32 from sheath 40. The guide is thenwithdrawn from sheath 40, leaving the sheath free to accept anytherapeutic tool, such as biopsy forceps.

Turning now to FIG. 7, there is shown an alternative implementation oftip portion 34, generally similar to that of FIG. 3, but in this caseincluding at least part of an imaging system, in this case an imagesensor 62. Image sensor 62 is shown here in a preferred implementationas an optical imaging sensor with a lens 64 positioned in front of animage sensor array 66. Illumination is preferably provided via an opticfiber light guide 68.

Given the strict limitations on dimensions of the sensor (requiring adiameter less than 2 mm), it is preferably implemented using CMOS or CCDimaging sensor technology integrated with lens 64 by micro-productiontechniques. Most preferably, image sensor 62 is integrated into locationsensor element 44. Specifically, the structure of the location sensorelement according to the most preferred implementation of the inventionincludes a plurality of coils 70 and their connecting wires 72,typically fixed in a block of adhesive 74. In this case, image sensor 62is preferably fixed in the same adhesive block. Optic fiber 68 may alsobe included in block 74, if lateral dimensions allow.

In some cases, production limitation and/or the lateral dimensions ofthe tip may not allow optic fiber 68 to extend through the sensor block.In this case, the preferred solution is to position optic fiber 68 withits end near the proximal side of block 74 which, at least in this case,is made of generally transparent, or at least somewhat translucent,material. In this case, sufficient light diffuses through the materialof block 74 around and between the suspended components to provideillumination of the field of view of image sensor 62 beyond the distalend of the assembly. A further alternative for providing illumination isto use at least a distal portion of sheath 40 as an optical waveguide.The illumination in this case may also be delivered by optic fiber 68terminating on the proximal side of block 74, by one or more lightsource mounted within guide element 32, or by a light source associatedwith handle 38 which delivers light directly to the proximal end ofsheath 40.

In other respects, tip portion 34 is similar to that of FIG. 3,including doubled-over steering wires 48 attached to base 46. Seen moreclearly here is a preferred subdivision of the flexible body 36 intofive internal lumens: one for each of the four steering wires and acentral lumen containing the electrical wires from the various sensorsand the optic fiber for illumination.

It will be clear that the addition of an image sensor to tip portion 34provides enhanced functionality as a small-gauge bronchoscope. As willbe discussed below, this configuration may be used to advantage withouta conventional bronchoscope. Nevertheless, given the image sensor sizerequirements and the limitations of current technology, the imagequality from sensor 62 will typically be significantly lower than thatof a conventional bronchoscope. For this and other reasons, it isenvisaged that image sensor 62 will be used primarily as an additionalenhancement to a device for use in conjunction with a bronchoscope,further facilitating navigation of the catheter of the present inventionbeyond the range of the bronchoscope.

Target Acquisition Techniques

In order to employ the location measurement system of the presentinvention as a navigational aid, it is necessary to identify one or moretarget location in the reference coordinate system. This may be donedirectly, or by importing location data from an offline source, such ascomputerized tomography (CT) data. Direct acquisition requires animaging device or other detector which can be used non-invasively tolocate the target. Importing targets from offline data requiresregistration of the offline data with the reference coordinate system.Various examples of both groups of techniques will now be described.

Isotopic Triangulation

FIG. 8 illustrates an arrangement for acquiring a target location in aposition sensor frame of reference using isotopic labeling and anexternal detector. According to this technique, a shot of isotopesolution is injected into the patient. The isotope is preferably thesame as those used in PET protocols. It is known in the art that, afterthe solution is absorbed by the body, its concentration in a lesion ishigher than in other parts of the body, thereby “marking” the lesion byelevated emission levels. In the case illustrated here, a lesion 80within the chest of patient 10 has been thus marked by injection of aradioactive isotope. A detector 82 coupled with a 6 DOF location sensorelement 84 is directed to sense this emission. Detector 82 is chosen tohave a directional sensitivity profile which allows identification of adirection towards a source of highest emission. In a simple case, thisis merely a detector with a direction of highest sensitivity, defined asthe “axis” of the detector, which is adjusted until it gives a maximumreading. Alternatively, given a sensitivity profile of the detector andreadings taken in a few different directions, a direction towards thesource of maximum emission may be derived mathematically. The multiplereadings may optionally be obtained simultaneously by a detector headwith multiple sensors. At each stage, the position and pointingdirection of the detector in the reference coordinate system is derivedby tracking system 22 based on outputs of location sensor element 84.

FIG. 9 illustrates the procedure for acquiring a target location usingan external detector such as in the arrangement of FIG. 8. First, atstep 86, a direction to the target is determined from a first point ofview. It will be appreciated that the combination of a direction towardsthe target (in this case, the direction to the source of maximumemission) and the position of the detector together define a line inspace passing through the target. Then, at step 88, the detector isrelocated to a new position and the direction to the target is againidentified, thereby defining a second line in space passing through thetarget. Optionally, this procedure is repeated from one or moreadditional detector positions (step 90). The intersection (or point ofclosest proximity) of all of these lines is then derived (step 92),thereby defining the position of the target in the reference coordinatesystem.

Fluoroscopic Triangulation

A similar technique can be used without isotropic labeling by use offluoroscopic imaging. Specifically, by replacing the detector 82 of FIG.8 which a fluoroscope system, it is possible to identify the targetwithin the image and designate the direction to the target. Here too,target direction designation may be achieved most simply by aligning thefluoroscope with a physical axis, typically indicated by crosshairs inthe display, aligned with the target. In all other respects, thetechnique proceeds exactly as described in FIG. 9 by defining thedirection to the target from two or more positions and identifying theintersection of the resulting lines as the target position.

Manual CT Registration

Although the isotopic labeling and fluoroscope-based solutions describedabove provide important solutions for cases where CT data is notavailable, it is generally believed to be highly preferable to integratethe system of the present invention with CT data.

By way of introduction, the use of CT as a diagnostic tool has nowbecome routine and CT results are now frequently the primary source ofinformation available to the practitioner regarding the size andlocation of a lesion. This information is used by the practitioner inplanning an operative procedure such as a biopsy, but is only availableas “offline” information which must typically be memorized to the bestof the practitioner's ability prior to beginning a procedure. As will bediscussed below, in addition to inputting target information,integration with the CT data provides important additional systemfunctionality, thereby greatly facilitating navigation to the targetlocation.

In contrast to the two prior methods, the CT data has its own system ofcoordinates. Matching the two system of coordinates, that of the CT andthat of the patient, is commonly known as registration. Registration isgenerally performed by identifying at least three locations in both theCT and on or inside the body, and measuring their coordinates in bothsystems.

Turning now to FIGS. 10-12, a first procedure according to the presentinvention for correlating CT data with a location measurement systemwill be described. Generally speaking, the technique as illustrated inFIG. 10 starts by generating from the CT data a simulated view of adistinctive feature within the branched structure (step 100) anddesignating a reference point viewed within the simulated view (step102). This is repeated (arrow 104) until at least three, and preferably5-10 CT reference points have been designated. Then, during performanceof a procedure on the patient, the bronchoscope or other image sensor ispositioned to view one of the same group of distinctive features (step106) so that the camera view corresponds to, and is generally similarto, a corresponding one of the simulated views. The operator thendesignates a reference point viewed within the camera view equivalent tothe corresponding reference point designated in the correspondingsimulated view (step 108), such as by contacting the point with theposition sensor element. Steps 106 and 108 are repeated (arrow 110)until three or more pairs of corresponding reference points areobtained. The designated reference points are then used to derive a bestfit registration between the computerized tomography image and thethree-dimensional frame of reference (step 112).

The implementation of this technique will be better understood fromFIGS. 11-12B. Prior to beginning the procedure, the volumetric CT datais stored and transferred to computer 24 or another suitably programmedmedical imaging workstation, either using the hospital Ethernet or froma data storage medium such as a compact disk (CD). The practitioner thenneeds to designate the required reference points. Preferably, thereference points used are easily identified anatomical landmarks,referred to a “fiducial points”. In principle, the fiducial points couldbe selected in a conventional two-dimensional “slice” display of the CTdata. In practice, however, this does not result in sufficientlyaccurate registration, as will now be explained.

The accuracy of the registration is dependent upon the ability toprecisely define and mark the reference points. In the bronchial tree,the available anatomical landmarks are the bifurcations of the bronchiwhich are up to a few centimeters in size for those at the entry of thebronchus. If these junctions are used as fiducial “points” or regions,the result would typically be very imprecise registration, unless verymany such points are taken. On the other hand, if the practitioner isrequired to match too many points, the entire procedure becomesinefficient. Accordingly, the present invention provides a technique forenhancing the ability of a practitioner to select equivalent pointswithin the region of the bifurcation at a much higher resolution thanthe overall dimensions of the bifurcation. Specifically, this is done byusing CT-based “virtual bronchoscopy” to generate simulated viewssimilar to the actual bronchoscope views. Virtual bronchoscopy is acomputer simulation technique in which CT data is used to construct avirtual model of airways within the body tissue, and this model is usedto generate simulated views similar to those viewed by a bronchoscope.The technology of virtual bronchoscopy is described in U.S. Pat. Nos.6,246,784 and 6,345,112 both to Summers et al., as well as thereferences cited therein, all of which are hereby incorporated herein byreference. In this context, the use of virtual bronchoscopy allows thepractitioner to employ his visual judgment based on factors such assymmetry and shape to designate equivalent reference points in both theCT data and the reference coordinate system with much greater precisionthan would otherwise be possible.

Turning now to FIG. 11, this shows a display screen from a preferredimplementation of a planning program which generates virtualbronchoscopy registration images for use in the present invention. Thedisplay as shown is divided primarily into four views. Three of theseviews display mutually perpendicular two-dimensional “slice” viewsderived from the CT data. The upper left view is an axial projection ofthe patient. The right upper view is a sagittal projection. The lowerleft view is an anterior-posterior (“AP”) view. In each view, acrosshair indicates the planes of the other two slices currentlydisplayed, all three planes intersecting at a point in the CT coordinateframe. In the lower right region, a virtual image of the bronchus at theselected point is displayed. In this case, the selected point is on thecarina, the upper junction of the bronchial tree. The software alsoallows adjustment of the viewing direction which, for this procedure, ischosen to be the direction from which a real bronchoscope will approachthe region.

As can be seen, the carina junction is long and does not in itselfdefine any single point. Nevertheless, by taking into account thesymmetry of the carina, a practitioner can designate a reference pointat a middle location along the carina, where the septum is relativelynarrow, in a repeatable manner with minimal error. This point is thenmarked as a selected fiducial point, and its coordinates in the CTcoordinate frame are stored. This procedure is repeated until at leastthree, and preferably between 5 and 10, fiducial points have beenrecorded. This data is preferably then stored or transferred in a formin which it can be made available for visual display to the practitionerduring the practical procedure.

Parenthetically, it will be noted that point selection in the simulatedimage is performed as selection of a point in the two-dimensional imageon screen using a mouse or other computer input device. Designation ofthe point in the three-dimensional CT data coordinate system is achievedby extrapolating from the selected point in the simulated viewingdirection until the line intersects the closest tissue surface(according to the aforementioned numerical model of a portion of thebody derived from the CT data).

During performance of the practical procedure, the first stored image ispresented to the practitioner who guides the bronchoscope to thecorresponding landmark feature within the patient. As the bronchoscopetip approaches the site, the bronchoscope views an image (FIG. 12A) verysimilar to the virtual image shown in the lower right panel of FIG. 11.The practitioner then designates the reference point, preferably byadvancing location sensor 44 located at the tip of locatable guide 32 totouch a point equivalent to the location marked in the virtual image(FIG. 12B) and designating the sensor position as the correspondingfiducial point in three dimensions in the reference coordinate system.This is repeated for a total of at least three, and preferably for all5-10, fiducial points designated in the virtual bronchoscopy stage. Onthe basis of the accumulated data, a best fit mapping (typically,translation and rotation) between the CT fiducial points and thereference coordinate system is derived. The possibility of a morecomplex distortion-correcting mapping will be discussed below withreference to FIG. 21.

Once a best fit mapping is derived, any and all information from the CTdata becomes readily available for importing into the locationmeasurement system frame of reference. Minimally, the location andpossibly also the shape of the lesion is incorporated as targetinformation by navigation software running on computer 24. Optionally,the data can also be used for importing a pre-planned route map to thetarget or to provide real-time CT and/or virtual bronchoscopy displayscorresponding to the current location sensor position, as will bediscussed further below.

Semi-Automated CT Registration

While the manual fiducial point designation of the above registrationtechnique is highly effective, the choice of number of points samplednecessarily represents a tradeoff between accuracy and efficiency. Inorder to circumvent this tradeoff and speed up the procedure, analternative semi-automated registration technique allows collection of alarge number of sample points automatically within a very short timeperiod. This technique will now be described with reference to FIGS.13-16.

In general terms, this technique is based upon automated collection ofmultiple reference points on the interior surface of an airway followedby fitting of a geometrical model (typically a cylinder) to thesepoints. Registration is then achieved by correlating this geometricalmodel to the corresponding feature(s) in a model based on the CT data.

Collection of the multiple reference point positions could be performedby moving position sensor 44 over regions of the surface directly. Morepreferably, the present invention provides a technique based on imageprocessing which allows collection of reference point positions simplyby advancing an image sensor associated with the position sensor alongthe airway.

Turning now to FIG. 13, this shows steps of a preferred method accordingto the teachings of the present invention for achieving registrationbetween computerized tomography data and a three dimensional frame ofreference of a position measuring system. The method begins by movingthe tip of the catheter along a first branch portion of the branchedstructure and deriving a plurality of images from the image sensor (step120). Each image is associated with corresponding position data of theposition sensor.

It will be noted that the image sensor may be either a conventionalbronchoscope imaging system, or an image sensor built in to the catheter30 of the present invention, such as is shown in FIG. 7. In either case,the spatial relation of the image sensor, including any lateral offset,must be determined before the procedure.

The images are then processed to derive position data for referencepoints on the surfaces of the tissue (step 122) and this position datais used to derive a best-fit of a predefined geometrical model to thefirst branch portion (step 124). Steps 120, 122 and 124 are thenrepeated for a second branch portion of the branched structure (step126). Alternatively, the geometrical model may be a combined model forboth branches in which case steps 120 and 122 are repeated first, andstep 124 is performed once for the amassed data. The geometricalmodel(s) are then correlated with the CT data to derive a best fitregistration between the computerized tomography data and the threedimensional frame of reference of the position measurement system (step128). In the simple case of two non-parallel branch portions eachmodeled as a cylinder, the two resulting cylinders are sufficient touniquely define a best fit mapping (translation and rotation) betweenthe CT and position sensor coordinate systems.

In a preferred implementation, step 122 is performed as follows. Imagestaken from different positions along each branch are correlated toidentify visible features which are present in plural images (step 130).These features may be any permanent or temporary visible features,including small blood vessels, localized variations in surface shape orcolor, and dust or other particles. For each of these features, acamera-to-feature direction is derived for each image showing thatfeature (step 132). These camera-to-feature directions and correspondingposition sensor data are then used to determine a feature position foreach visible feature (step 134).

This process is illustrated graphically in FIGS. 14A-16. FIGS. 14A and14B illustrate schematically camera views taken from two differentpositions, a feature 136 being visible in both views. FIGS. 15A and 15Brepresent the corresponding positions of catheter tip 34 (with imagesensor 62 and location sensor 44) from which these views were taken. Itwill be noted that the position of a feature in the camera view maps toa unique direction from the camera to the feature. Thus, bypredetermining the optical characteristics of the camera (either bydesign, or by a calibration procedure such as by using a hemisphericaldome with lights), the feature position in the image can be converted toa direction vector. In FIGS. 15A and 15B, this is illustratedschematically as off-axis angle (6|, 82). The real data also includes asecond angle (rotation angle about the axis) together defining a uniquecamera-to-feature direction. By combining this information with the 6DOF position sensor data (and any offset adjustment) from two positions,the feature position in three-dimensional space can readily be derivedby simple triangulation, as shown in FIG. 16. Where data from more thantwo positions is available, it can be used to further improve accuracy.

Although illustrated here schematically for a single isolated feature,it is typically possible to derive tens, or even hundreds, of suchfeature positions from a length of airway. This allows an enhanced levelof precision in the correlation procedure.

As before, once a best fit mapping is derived, any and all informationfrom the CT data becomes readily available for importing into thelocation measurement system frame of reference. Minimally, the locationand possibly also the shape of the lesion is incorporated as targetinformation by navigation software running on computer 24. Optionally,the data can also be used for importing a pre-planned route map to thetarget or to provide real-time CT and/or virtual bronchoscopy displayscorresponding to the current location sensor position, as will bediscussed further below.

Navigation Techniques Tip-to-Target Displays

Once a target location has been identified in the reference coordinatesystem, by one of the above techniques or otherwise, the device of thepresent invention is ready to assist in navigation to the target. Thesmall air paths in the periphery of the lung are generally notdetectable by the currently available real-time imaging devices.According to certain aspects of the present invention, the systemprovides tip-to-target displays and various other navigation aids tofacilitate navigation to the target beyond the reach of the imagingsystem of a conventional bronchoscope.

Thus, according to a preferred method according to the present inventionfor steering a catheter through a branched structure to a targetlocation, a representation is displayed of at least one parameterdefined by a geometrical relation between the pointing direction of thetip of the catheter and a direction from the tip of the catheter towardsthe target location, while the catheter is moved within the branchedstructure. The at least one parameter preferably includes one or more ofthe following parameters: an angular deviation between the pointingdirection of the tip of the catheter and a direction from the tip of thecatheter towards the target location; a direction of deflection requiredto bring the pointing direction of the catheter into alignment with thetarget location; and a distance from the tip of the catheter to thetarget. It should be noted that each of the aforementioned parameters isa useful navigation aid in its own right. The angular deviation, even ifappearing just as a numerical angle without any display of direction,can be used by trial and error to find a steering direction whichreduces the deviation. Similarly, the direction of deflection can beused as a steering aid, even without a direct indication of the angulardeviation. The distance to the target is also an important indicator ofincreasing proximity to the target. In a most preferred implementation,both the angular deviation and the direction of deflection aredisplayed, typically also with an indication of the distance to thetarget.

One particularly preferred display format is illustrated in FIGS. 17Aand 17B which shows at least one of the parameters in the context of arepresentation of a view taken along the pointing direction of the tipof the catheter. This representation does not require any imagingsystem, being generated numerically from the 6 DOF location informationfor the catheter tip, the patient's body, and the target location.

The display as illustrated has three zones. The first is a circulardisplay analogous to the straight-ahead viewing direction of abronchoscope imaging system, but instead displaying graphicallyinformation regarding the direction to the target. In the case of FIG.17A, the target is outside the forward-region defined by the circle. Inthis case, the required deflection direction to point towards the targetis indicated by arrows 140. The orientation of the display is taken withthe “up” steering direction of the catheter at the top of the display sothat the practitioner can relate the display to the steering mechanismcontrols. The lower-right region of the display shows a pictogram 142which illustrates graphically the relation of the “up” steeringdirection to the patient's body. Thus in the example of FIG. 17A, thecatheter tip is currently pointing downwards towards the patient'sback-left side with the “up” direction turning towards his chest. Thethird zone is an alphanumeric display which provides numerical data suchas the angular deviation 144 to the target and the distance 146 to thetarget.

FIG. 17B shows the display after further advance of the catheter. Inthis case, the angular deviation is already sufficiently small that thetarget, as represented by symbol 148 appears within the circulardisplay. In this case, pictogram 142 indicates that the “up” steeringdirection is actually currently towards the patient's back, i.e., downrelative to the patient lying on the operating table.

Preferably, the pointing direction display of FIGS. 17A and 17B issupplemented with various additional displays which facilitateinterpretation by the practitioner during use, and provide variousadditional information or functionality to the practitioner. By way ofexample, FIGS. 18A-18C show computer graphic representations of thecatheter tip 150 and target 148 in sagittal, AP and axial projections,respectively. (The additional lines appearing in these figures will bediscussed below.) FIG. 19 shows a further example in which thetip-to-target display of FIG. 17A is combined with dynamic CT-baseddisplays corresponding to axial, sagittal and AP planes passing throughthe current catheter tip position. A further preferred option (notshown) replaces or supplements the “slice” CT displays with a virtualbronchoscopy image corresponding to the current position and pointingdirection of the catheter tip, thereby offering simulated functionalityof a small gauge imaging catheter. In the case that catheter 30 isimplemented with an image sensor 62 as in FIG. 7, the real image fromthe sensor is preferably provided.

Route Planning

Optionally, the CT or virtual bronchoscopy information can be used topre-select a planned route to the target. Specifically, a series oflocations may be selected on the CT slices, for example by use of acomputer mouse. Each location is actually a coordinate in 3D space (twocoordinates within the image and the third coordinate from the locationof the slice itself). By connecting these locations, it is possible todraw a path in 3D space. If each location is taken from adjacentportions of interconnected air pathways inside the bronchial tree tracedbackwards from a target position to the bronchus (the entrance of thebronchial tree), the resulting path corresponds to a “roadmap” of aplanned route to the target. This route, or steering data based upon theroute, is then displayed together with the target data during theprocedure.

The feasibility of route planning of this type depends upon the positionof the target and the resolution of the CT data available. In certaincases, the distance between adjacent slices in the CT data is such thatthe course of the very fine airways between adjacent slices cannot bereliably determined. This problem can typically be addressed by using athinner slice thickness where this is possible.

History

It is the nature of the maze of the bronchial tree that a branch whichextends locally towards a target location does not actually lead to thetarget. As a result, a practitioner may frequently find that he hassteered into a branch which looked promising but then leads away fromthe target. In such circumstances, it is valuable to provide anavigation aid to avoid repetition of the error, and to help identifythe correct path. For this purpose, the system of the present inventionand the corresponding method preferably provide a “record” functionwhich allows selective display of a historical path traveled by thecatheter tip.

Specifically, referring to FIGS. 18A-18C, there is shown a pathrepresented by a solid line 152 in all three views. Path 152 representsa path previously followed by the practitioner in trying to reach target148. Although starting in what appeared the right direction to reach thetarget, the practitioner found that the path lead to a positionposterior to the desired target. At that point, the practitioneractuated the recording mode and withdrew the catheter, therebygenerating a line 152 indicative of the path already followed. Thepractitioner then starts to advance the catheter again slowly, feeling(via the steering mechanism) for an upward branch until he finds thecorrect route indicated by dashed line 154 which branches off upwardsfrom path 152.

Cyclic Motion Correction

Although the catheter position is measured via location sensor 44 inreal time, the target location is not. The target is generallyconsidered fixed relative to the patient's body position which ismonitored in real time by sensors 20 (FIG. 1). However, navigationaccuracy may decrease as a result of cyclic chest movement resultingfrom breathing. Preferably, precautions are taken to reduce the effectsof this cyclic movement. This may be done by one of a number oftechniques, as follows.

According to a first preferred option, position sensor measurements aresampled selectively so that measurements are only made at an extreme ofa cyclic motion. The extremes can readily be identified by the cyclicdisplacement of sensors 20 during the breathing cycle. It may bepreferred to use the maximum exhalation state for measurements sincethis state typically remains steady for a relatively larger proportionof the breath cycle than the maximum inhalation state.

Alternatively, measurements can be taken continuously, and the cyclicvariations eliminated or reduced by additional processing. Thisprocessing may include applying a low-frequency filter to themeasurements. Alternatively, an average of the measurements over a timeperiod of the cyclic motion may be calculated.

Local Distortion Correction

Various techniques were discussed above for achieving registration(translation and/or rotation) of CT data with the reference coordinatesystem of the measurement system so as to make the CT data available forimporting target information and providing real time CT or virtualbronchoscopy displays. In many cases, however, a translation androtation mapping is not fully satisfactory, especially in regions farfrom the reference points used to perform registration.

The primary cause of the mismatch between the two coordinate frames isbelieved to be body posture distortion resulting from the different bodypostures used for the two procedures. Specifically, in order to maintainconstant position during CT scanning, the patient is typically requiredto hold his breath for the duration of scanning (either in one pass, orsubdivided into a number of periods). Furthermore, the patient isrequired to lift his arms above his head to avoid artifacts which wouldbe caused by the arms within the scanning region. In contrast, abronchoscopy procedure is performed over an extended period andtypically under partial sedation, making it infeasible to request eitherholding of the breath or raising of the arms for the entire procedure.

A particularly simple but practical approach to addressing this problemis illustrated schematically in FIGS. 20A-20D. It is assumed that, byrequesting that the patient temporarily breath in and raise his arms, itis possible to closely reproduce the body posture and geometry underwhich the CT scan was performed. This state is represented schematicallyin FIG. 20A. The “normal” relaxed state of the patient is representedschematically in FIG. 20B. This allows the practitioner to perform asimple localized correction by measuring the position of the cathetertip 160 in the state of FIG. 20A, measuring it again in the relaxedstate of FIG. 20B, and using the difference (arrow 162) as a correctionvector by which all the CT data is then shifted (FIG. 20D). Thisprocedure can be repeated quickly and easily as many times as required,each time effectively re-aligning the CT data with the region where thecatheter tip is currently positioned.

FIG. 21 illustrates an alternative approach to this issue in which amore comprehensive distorting transformation is used to map the CT datato the current body posture. The data for deriving the requiredtransformation may in principle be derived from repeated measurements asdescribed with reference to FIGS. 20A-20D. Alternatively, wheresufficient data is available from the initial registration procedure (byone of the aforementioned registration techniques, or from analternative source), the entire registration adjustment can be performedfrom the outset as a distorting transformation which compensates for thebody posture related distortion.

Use of Tools

As mentioned earlier, once catheter 30 has successfully been navigatedto the target location, guide element 32 is preferably removed, leavingsheath 40 in place as a guide channel for bringing a tool to the targetlocation. In order to ensure stability of the sheath and accurateguidance of a tool to the target, the present invention provides apreferred of use as illustrated in FIG. 22.

Specifically, FIG. 22 illustrates a preferred method of guiding amedical tool through a branched structure to a target location, wherethe guide element is first locked within the sheath so as to preventmovement of the guide element relative to the sheath (step 170). Thesheath and guide element are then inserted through the working channelof a handle (e.g. part of a bronchoscope) and navigated to the targetlocation (step 172), such as by the techniques described above. Thesheath is then locked within the working channel to prevent relativemovement of the sheath relative to the handle (step 174). The guideelement may then be unlocked and withdrawn from the sheath (step 176).This leaves the lumen of the sheath in place as a guide for insertion ofa tool to the target location (step 178).

Sheath 40 may be used as a guide for insertion of substantially anymedical tool. Examples include, but are not limited to, biopsy toolssuch as various kinds of forceps and aspiration needles, and varioustools used for ablating malignant tissue that are used in context of abronchial procedures. Parenthetically, it should be noted that the term“tool” is used herein to refer to the entirety of the elongatedstructure part of which is inserted along the sheath, and not just theactive tip portion. Most standard tools for use via the working channelof a bronchoscope have an external diameter of up to about 1.8 mm,allowing them to fit readily through the lumen of sheath 40.

As an additional safeguard to ensure that the sheath does not getdislodged from the target during withdrawal of the guide element andinsertion of a tool, a selectively actuatable anchoring mechanism ispreferably associated with a portion of the sheath. The position of theanchoring mechanism along the sheath is generally not critical. Wherethe target location is in the small diameter airways beyond the reach ofa conventional bronchoscope, lateral displacement of the sheath from thetarget is typically not a problem. It is therefore sufficient to provideanchoring against longitudinal displacement which may be provided in thebronchus or in the nose. Structurally, the anchoring mechanism ispreferably implemented as an inflatable element. Alternatively, amechanically deployed anchoring element may be used. In either case,anchoring mechanisms suitable for this purpose are known in the art.

As a further optional precaution, sheath 40 is preferably provided witha radio-opaque marker to facilitate verification that it has not movedby fluoroscopic imaging. According to a first preferred option, themarker is implemented by treating a distal part of the sheath so as torender it substantially radio-opaque. Alternatively, at least oneradio-opaque marker may be attached near or at a distal end of thesheath.

As already mentioned, the present invention can be used withsubstantially any standard tool. In order to ensure the correct extentof insertion of the tool along sheath 40, it may be preferable to firstcalibrate the length of the tool. This is preferably performed byinserting the tool before use into a calibration tube which has a lengthcorresponding to a length of the lumen of sheath 40 and marking anextent of insertion on the tool. Marking can be performed simply byapplying an “INSERT THIS FAR” sticker to the elongated body of the tool.Alternatively, a clip or the like can be applied to physically obstructover-insertion of the tool.

In principle, calibration of the tool could be performed using thesheath itself prior to the procedure. It is generally consideredpreferable, however, to avoid unnecessary wear on the components to beused in the procedure. Instead, as illustrated in FIG. 23, the guideelement and sheath are preferably supplied in a coiled storage tube 180which doubles for use as a calibration tube for calibrating the lengthof a tool 182. The practitioner then removes the guide element andsheath from storage tube 180 and inserts tool 182 until the end of thetool reaches the end of storage tube 180. The practitioner then markstool 182 with a sticker or clip 184 as described earlier. Tool 182 isthen ready for use.

Miniature Endoscope with Retractable Imaging

As exemplified above with reference to FIG. 7, certain embodiments ofthe present invention provide a catheter 30 made up of a sheath 40having a lumen extending from a proximal insertion opening to a distalopening, and a guide element 32 configured for insertion through sheath40, where the guide element includes at least part of an imaging system62, and the catheter includes at least one steering mechanism forco-deflecting sheath 40 and guide element 32. It should be noted thatthis structure, with or without a location sensor, is a highlysignificant stand alone device with robust functionality.

Specifically, the use of a sheath with a retractable imaging systemcombines the advantages of a small gauge single lumen catheter with thecapabilities of both endoscopic imaging, steerable navigation and toolaccess. The devices preferably include an optical imaging sensor, suchas sensor 62 described above, or part of an optical imaging system suchas a light fiber bundle.

A range of variants implementations of such a stand alone device arewithin the scope of the present invention. Firstly, it should be notedthat the steering mechanism may be a conventional unidirectionalsteering mechanism, and may optionally be included within the sheathrather than the guide element. More preferably, a multi-directionalsteering mechanism such as that of FIGS. 3-5C is used. Both here and inthe above-mentioned embodiments, it should be noted that the steeringmechanism may optionally be incorporated within the sheath rather thanin the retractable guide element. This provides advantages particularlywhere the target location is reached by maintaining deflection of thecatheter tip, allowing this deflection to be maintained duringretraction of the guide and insertion of a tool. A similar result may beachieved by including a second steering mechanism or another mechanicalarrangement for “freezing” the state of curvature of the tip of thesleeve, as an addition to the steering mechanism of the retractableguide. This, however, is at the cost of increased sleeve thickness andincreased cost.

The device may be combined to advantage with the location measurementsystem described above, allowing it the full functionality of the systemdescribed above without requiring a bronchoscope. All of the optionsdiscussed above regarding the image sensor and illumination arrangementare also available here.

As with the aforementioned use of sheath 40, the sheath is preferablyprovided with a selectively actuatable anchoring mechanism such as thosediscussed above. Radio-opaque distal marking may also be used toadvantage.

Finally, an alternative embodiment of the device includes a retractableradioactivity sensor which can be withdrawn from the sheath with theguide element. Here too, this is of value as a stand-alone devicecombining the functionality of both a radioactivity sensor and a toolguide in a single lumen device.

It will be appreciated that the above descriptions are intended only toserve as examples, and that many other embodiments are possible withinthe spirit and the scope of the present invention.

1-11. (canceled)
 12. A method of steering a locatable guide of acatheter assembly comprising: rotating an actuator relative to a handleof the catheter assembly to select one or more steering elements from aplurality of steering elements, the plurality of steering elementsextending between the handle and a distal end of a locatable guide andconfigured to articulate the distal end of the locatable guide; andsliding the actuator relative to the handle to actuate the selected oneor more steering elements to articulate the distal end of the locatableguide.
 13. A method according to claim 12, wherein rotating the actuatorrelative to the handle includes aligning a step of the actuator with theselected one or more steering elements.
 14. A method according to claim13, wherein rotating the actuator relative to the handle includesaligning the step with two adjacent steering elements of the pluralityof steering elements to select the two adjacent steering elements.
 15. Amethod according to claim 13, wherein when the actuator slides relativeto the handle, the step of the actuator engages the selected one or moresteering elements to slide the selected one or more steering elementsrelative to the handle.
 16. A method according to claim 12, whereinrotating the actuator relative to the handle includes aligning aclearance slot of the actuator with one or more steering elements of theplurality of steering elements that are not selected.
 17. A methodaccording to claim 16, wherein each steering element includes a flangeand the clearance slots are aligned with the flanges of the one or moresteering elements that are not selected when the actuator is rotatedrelative to the handle.
 18. A method according to claim 17, wherein whenthe actuator slides relative to the handle, the one or more steeringelements that are not selected remain in place due to alignment of theflanges with the clearance slots.
 19. A method according to claim 12,wherein sliding the actuator relative to the handle includes sliding theactuator from a first position to a second position, the second positionlocated proximal of the first position.
 20. A method according to claim11, wherein rotating the actuator relative to the handle of the catheterassembly includes rotating the actuator to select one of: a first of thesteering elements to articulate the distal end of the locatable guide ina first direction, a second of the steering elements to articulate thedistal end of the locatable guide in a second direction, or both thefirst and the second of the steering elements to articulate the distalend of the locatable guide in a third direction intermediate to thefirst direction and the second direction.